1. Field of the Invention
The present invention relates to the field of electrode materials, and more specifically, to a carbon-deposited alkali metal oxyanion electrode material as well as to a process for preparing same.
2. Description of the Related Art
Positive electrodes of lithium-ion battery generally comprise an electrochemically active cathode material, a binder and carbon particles which act as an electronically conductive additive. During battery cycling, it has been observed that such positive electrodes generally show a deleterious increase in electrode resistance. It has been proposed that as the number of cycles increases, the cathode material exhibits unit lattice volume expansion/shrinkage variations that are due to insertion/deinsertion of alkali cation in the cathode material. It is believed that these variations induce a loss of electronically conductive network contact with the cathode material and/or breaking of cathode material particles. As a result, the battery's capacity decreases and the battery has a resulting shorter life span.
To address this problem, it has been proposed to fine-tune the composition of cathode materials in order to reduce the observed change of unit cell volume concomitant to alkali cation insertion/deinsertion.
WO 2009/096255 (assigned to Sharp Kabushiki Kaisha), which is incorporated herein by reference in its entirety, describes a LiyKaFe1-xXxPO4 cathode material with reduced change of the unit cell volume, where X represents at least one element selected from group 2 to 13 elements; a and x are 0<a≦0.25 and 0≦x≦0.25, respectively; and y is (1−a).
WO 2010/134579 (assigned to Sharp Kabushiki Kaisha), which is incorporated herein by reference in its entirety, describes an alkali metal phosphosilicate material of general formula LiFe1-xMxP1-ySiyO4 where the average valency of Fe is +2 or greater; M is an element having a valency of +2 or greater and is at least one selected from the group consisting of Zr, Sn, Y and Al; the valency of M and the average valency of Fe are different; 0<x≦0.5; and y=x*(valency of M−2)+(1−x)*(average valency of Fe−2).
JP 2011/77030 (assigned to Sharp Corp. and Kyoto University), which is incorporated herein by reference in its entirety, describes an alkali metal phosphosilicate material of general formula Li(1-a)AaFe(1-x-b)M(x-c)P(1-y)SiyO4 where A is at least one kind selected from a group consisting of Na, K, Fe and M. Average valence of Fe is +2 or more, M is an element of valence of +2 or more, and at least one kind selected from a group consisting of Zr, Sn, Y and Al, the average valence of M and the average valence of Fe are different from each other, 0<a≦0.125, the total number of moles of Na and K in A is d, number of moles of Fe in A is b, number of moles of M in A is c, a=b+c+d, 0<x≦0.5, and 0<y≦0.5.